Manganese, superoxide dismutase, and oxygen tolerance in some lactic acid bacteria

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Abstract
The aerotolerant bacterium Lactobacillus plantarum, which lacks superoxide dismutase (SOD), possesses a novel substitute for this defensive enzyme. L. plantarum contains 20-25 mM Mn(II), in a dialyzable form, which is able to scavenge O2- apparently as effectively as do the micromolar levels of SOD present in most other organisms. A survey of the lactic acid bacteria (including L. plantarum, L. fermentum, L. bulgaricus, L. acidophilus, L. ruminis, L. mesenteroides, Aerococcus viridans, Pediococcus pentosaceus, Streptococcus lactis, S. faecalis and S. sanguis; Escherichia coli was also studied) is described. The substitution of millimolar levels of Mn(II) for micromolar levels of SOD is a common occurrence in this group of microorganisms, which contained either SOD or high levels of Mn(II), but not both. Two strains, which had neither high levels of Mn(II) nor SOD, were very oxygen intolerant. Lactic acid bacteria containing SOD grew better anaerobically than anaerobically; the organisms containing Mn(II) in place of SOD showed aerobic growth which was, at best, equal to anaerobic growth. Plumbagin (5-hydroxy-2-methyl-1,4-naphthoquinone) increases the rate of O2- production in these organisms. Lactobacillus strains containing high intracellular Mn(II) were more resistant to the oxygen-dependent toxicity of plumbagin than were strains containing lower levels of Mn(II). A high internal level of Mn(II) evidently provides these organisms with an important defense against endogenous O2-.